Which of these numbers is prime? ${43,\ 49,\ 69,\ 70,\ 93}$
Answer: A prime number has exactly two factors: 1 and itself. The factors of 43 are 1 and 43. The factors of 49 are 1, 7, and 49. The factors of 69 are 1, 3, 23, and 69. The factors of 70 are 1, 2, 5, 7, 10, 14, 35, and 70. The factors of 93 are 1, 3, 31, and 93. Thus, 43 is a prime number.